piRNA-deficient Maelstrom (Mael) null mice are characterized by a strong upregulation of retrotransposon LINE-1 (L1) in meiotic spermatocytes. This defect turns out in the accumulation of L1 RNA and ORF1p in their cytoplasm and the formation of prominent ribonucleoprotein aggregates. We used 3-months-old Mael-/- male mice to characterize the protein composition of those ORF1p aggregates.